Damn, I did it again! Pete Seeger set the letter to music in 1951, and titled it "Sacco's Letter to His Son." Is that the letter you are referring to Jim?

Here is a link to the lyrics at Jim Capaldi's Pete Seeger appreciation page:

http://ourworld.compuserve.com/homepages/JimCapaldi/sacco.htm

You can find more info on the song in Pete's autobiography "Where Have All the Flowers Gone" if I'm remembering correctly.

Holly Near & Ronnie Gilbert did "Two Good Arms" on their excellent "Lifeline" album.

Woody's song is titled "Two Good Men" from the "Ballads of Sacco & Vanzetti" album, put out by Moses Asch on Folkways. You can go hear to read about it (Woody wasn't happy with the results of his songwriting, and never finished the project):

http://www.geocities.com/Nashville/3448/sacco.html#hisbg